Ultrasonic lapping machines



June 18, 1963 1 BALAMUTH ETAL 3,093,937

ULTRASONIC LAPPING MACHINES Filed Nov. 30, 1962 4 Sheets-Sheet 1 Z /9 Z L 1 D I vl' w1 'f- I l," 26j/W7 INVENTORS 171g l.. LEw/s BALAMUTH s.

ARTHUR KURIS ATTORNEY.

June 18, 1963 L. BALAMUTH ETAL ULTRASONIC LAPPING MACHINES Filed NOV. 30, 1962 4 Sheets-Sheet 2 F'j 3. l 54 3f f2 s /7 69 ya INVENTORS LEWIS BALAMUTH & ARTHUR KURIS AT TORNE Y.

June 18, 1963 LLLLL AM TTTTT Al. 3,093,937

June 18, 1963 L. BALAMUTH r-:rAL 3,093,937

ULTRAsoNIc LAPPING MACHINES Filed Nov. 30, 1962 4 Sheets-Sheet 4 INVENTORS LEWIS BALAMUTH a ARTHUR KuRls ATTORNEY.

United States Patent 3,093,937 ULTRASONIC LAPPING MACHINES Lewis Balamuth, New York, and Arthur Kuris, Bronx, N.Y., assignors to Cavitron Ultrasonics Inc., Long Island City, N.Y., a corporation of New York Filed Nov. 30, 1962, Ser. No. 241,330 19 Claims. (Cl. 51--67) This invention relates generally to lapping machines for producing substantially perfectly smooth `surfaces or mirror finishes on hard objects, and more particularly is directed to machines employing high frequency, preferably ultrasonic vibrations for the lapping operation.

In most existing lapping machines, the workpieces are pressed against a lap plate which is continuously rotated while a lapping compound consisting of a slurry of a suitable abrasive in a liquid carrier is supplied to the surface of the lap plate to smoothly finish the surfaces of workpieces pressed against the latter. The workpieces are usually rotated or made to follow orbital paths which are eccentric with respect to the axis of rotation of the lap plate in an effort to ensure that the wear on the latter and the lapping action on the workpieces will be uniform.

The main disadvantages of the above described existing lapping machines are the relatively slow rate of stoel; removal from the workpieces so that the lapping operation is time consuming and hence relatively costly, and also the high rate of wear of the lap plate which requires relatively frequent resurfacing or replacement of the lap plate. Since the lapping action results from the rotational movement `of the lapping plate with respect to the workpiece or pieces while the latter are strongly pressed against the lap plate, the lapping action is obviously accompanied by considerable frictional heating of the workpieces which may result in burning or distortion of the latter, particularly when the workpieces are thin members. The foregoing disadvantages of the existing lapping machines are particularly accentuated when the workpieces are `of hard materials, for example, wafers of germanium or silicon which are to be lapped to a small and uniform thickness prior to being diced into blanks or semi-conductor elements intended to function as rectiers, transistors, photodiodes or the like.

Accordingly, it is an object of the present invention to provide lapping machines which are free of the stated disadvantages of the existing machines, and more particularly which are capable of achieving a high rate of stock removal, even when the workpieces are of hard material and are applied with a relatively light pressure against the lap plate, while avoiding or substantially minimizing wear of the lap plate and frictional heating of the worlcpieces so that the latter can be finished to an extremely small thickness without the danger of burning or distorting the workpieces.

ln accordance with an important aspect of this invention, the lap plate is in the form of a circular ring which is vibrated radially at a high or ultrasonic frequency and with an `amplitude that is uniform about the entire circumference of the ring, and the workplaces are pressed against the annular surface of the vibrated ring and made to move along orbital paths which are eccentric with respect to the center of the vibrated ring, while a suitable abrasive slurry is applied evenly between the annular surface of the vibrated ring and the workpieces to polish or lap the surfaces of the latter in response to the high frequency or ultrasonic vibration of the lap plate.

Another object is to provide lapping machines of the described character in which the circular ring which is radially vibrated has its annular lapping surface formed with grooves, at least some of which preferably extend at substantial angles to the directions of the radial vibrations, so that the transmission of the vibrational energy to the lapping compound is promoted by the grooves to effect cavitation thereof and thereby increase the rate of stock removal from the workpieces while wear on the lap plate is substantially minimized. Further, the grooved annular surface of the radially vibrated lap plate promotes the uniform ydistribution of the lapping compound between the workpieces and the annular lapping surface and thereby ensures uniform stock removal from the workpieces 4and uniform wearing of the lap plate, to the limited extent that such wear does occur, thereby to both improve the finish produced on the Workpieces and to increase the useful life of the lap plate.

The above, and other objects, features and advantages of the invention, will be apparent in the following detailed description of illustrative embodiments thereof which is to be read in connection with the accompanying drawings forming a part hereof, and wherein:

FIG. l is a vertical sectional View of an ultrasonic lapping machine embodying the present invention, which view is tal/en along the line l-Il on FlG. 2;

FlG. 2 is a top plan view of the lapping Imachine of FIG. l;

FIG. 3 is an enlarged axial sectional view of the unit for effecting radial vibration of the circular ring constituting the lap plate in the machine of FGS. l and 2;

FlG. 4 is an enlarged, fragmentary sectional view corresponding to a portion of FlG. l, and showing details of the structure of the lapping machine;

FIG. 5 is 'an enlarged, fragmentary sectional View taken along the line 5-5 on FIG. l;

FIGS. 6, 7 and 8 are plan views of lap plates for use in ultrasonic lapping machines embodying this: invention, and having different patterns of grooves in the'annular lapping surfaces thereof;

FIGS. 9, l0, l1 and l2 are greatly enlarged sectional views illustrating the cross-sectional shapes of grooves that may be formed in the annular surface of the vibrated lap plate in accordance with the patterns of any of FIGS. 6, 7 and 8;

PG. 13 is a view similar to that of FlG. l, but illustrating another embodiment of the invention; and

FIG. 14 is a top plan view, partly broken away and in section, of the ultrasonic lapping machine of FlG. 13.

Referring to the drawings in detail, and initially to FIGS. l and 2 thereof, it will be seen that an ultrasonic lapping machine embodying the present invention and there generally identified by the reference numeral l0 may include an upwardly opening housing 1l having a partition l2 extending horizontally thereacross at a location intermediate the top of the housing and the bottom wall 13 of the latter so .as to divide the housing into an upwardly opening space 14 and a lower compartment 15.

A circular ring 16 constituting the lap plate of machine l@ is disposed within the upper space 14 immediately above partition l2. The circular ring 16 is made to vibrate radially, as hereinafter described in detail, by means of a vibration generating unit l7.

As shown on FIG. 3, the vibration generating unit 17 includes a transducer 18 which is made to vibrate at high frequency and low amplitude when subjected to the influence of a corresponding high frequency alternating magnetic field generated by .a surrounding winding i9. The longitudinal vibrations thus induced in transducer 13 are transmitted through a connecting body 2l) to the ring 16. The body 20 is preferably shaped, formed and designed as an acoustic impedance transformer, that is, to act as a vibration amplitude magnifier so that the amplitude of the vibrations transmitted radially from transformer 20 to ring 16 is substantially greater than the amplitude of the vibrations received from the transducer l5. As eX- plained in greater detail in US. Letters Patent No. 2,792,674, issued May 2l, 1957, to the assignee of the 'a a present application, the input portion of body Ztl may have a greater mass than the output portion thereof in order to obtain the desired magnication of the vibration amplitude.

The transducer 18 may be any one of a number of electromechanical types, such as, electrodynamic, piezo electric or magnetostrictive. The operating frequency may be in the higher sonic or ultrasonic ranges, but preferably is of the order of 20,080 to 100,000 cycles per second. At these preferred frequencies, a transducer l of the magnetostrictive type is most desirable. rEhe transducer 18 may be formed of a stack of plates or laminations of a metal, such as, nickel, Permanickel, Permendur, or other metals which have high tensile strength and are highly magnetostrictive in character, so that the transducer will longitudinally vibrate to a maximum degree when subjected to the influence of an alternating magnetic field established when biased alternating current is supplied to the winding i9 in surrounding relation to the transducer.

The transformer or connecting body Ztl is rigidly secured at the input end thereof to the transducer ld by brazing, silver solder or other permanent fastening means. The other or output end of transformer Ztl may be provided with a threaded bore 21 for receiving a mating stud 22 which projects radially from the outer periphery of ring 16 and constitutes the means for connecting the vibration generating unit 17 to the lapping ring. The output end of transformer or connecting body 2@ may be provided with a polygonal cross-section, as at 23, to receive a wrench or the like by which the transformer may be tightened on the stud 22.

The magnetostrictive transducer 18 and the input portion of the transformer or connecting body Ztl are contained within a generally tubular casing member 2d of nylon or similar non-conductive, liquid impervious material that will not interfere with the magnetic field set up by the winding or coil 19 wound thereon. The end of tubular casing member Z4 from which transformer 2h projects is retained within a mounting block 25, for example, by means of set screws (not shown) in the block, and a fluid-tight seal is provided therebetween by means of a sealing ring 26. The transformer or connecting body V20 is also mounted in the block Z5 by means of a flexible sealing ring 27 retained in .a suitably provided groove in the exterior surface or periphery of body 2d. The ring 27 is preferably disposed at a nodal point of the longitudinal vibrations transmitted through body 2d, which nodal point is approximately midway between the ends of the body 2th when the latter has a preferred length equal to an integral number `of half wavelengths of the vibrations or standing compressional waves developed therein at the operating frequency. Further, the sealing and mounting ring 27 is secured against a cooperating shoulder within the block by means of a retaining ring 2d held in position by a threaded plug 29.

The block 25 is secured, as by bolts fr@ (FlG. 1), to a bracket 31 extending outwardly from a side wall of housing 11 so that the axis of vibration generating unit 17 is directed horizontally and the output end portion of connecting body 2d passes ythrough a suitable opening provided in the side wall of housing 11 above bracket 31. `Such opening in housing 11 is preferably sealed around the transformer or connecting body 20 by a ilexible sealing ring 32 engaging the surface of body Ztl and being mounted in a retainer 33 which is Welded or otherwise secured to the side wall of housing lll around the opening in the latter.

To achieve most efficient operation of the vibration generating unit 1'7, the transducer 1S and the connecting body or transformer 2i) are each formed with a length equal to an integral number (preferably l) of half wavelengths of sound in the respective materials thereof at the desired frequency of vibration.

Suitable alternating current to effect vibration of the transducer 18 is supplied Ito the winding 19 through wires 3ft (FIG. 3) extending from a suitable alternating current generator (not shown).

Since heat is generated when vibrations are induced in the transducer 1S and the most emcient operation of the latter is obtained when overheating thereof is avoided, a gaseous or liquid coolant is preferably continuously supplied to the interior of the tubular casing member 2d by way of a conduit or tube 35 opening into the end of the casing member remote from mounting block 25.V The return for the coolant its provided by means of a tube or conduit 36 communicating with `a duct 37 formed in mounting block 25 and opening into the annular space defined between connecting body 2@ and casing member at a location intermediate the sealing rings 26 and 27.

The lapping ring 1o is preferably formed from la solid circular block yof material softer 'than that constituting the worlipieces to be lapped and yet capable of eiliciently transmitting the vibrations, such as, aluminum or magnesium alloy, and soft bronzes. .The ring 16 is formed with a circular hole in the center thereof, and preferably has an outer diameter and inner Vdiameter which are selected, as hereinafter described in detail, so that the longiitudinal vibrations occurring at the output end of connecting body 2@ of unit 17 and transmitted radially into ring 16 at one point on the periphery of the latter are effective to cause radial vibration of ring 16 uniformly around the entire circumference of the latter, with a loop of such radial vibrations occurring adjacent the outer `periphery of the lapping ring. Such radial vibrations occur substautially in a horizontal plane and cause the ring 16 to be diametrically expanded and contracted during each vibrational cycle.

The lapping ring 16 is suitably suppouted on partition vZ `of housing 11, for example, by three equally, angularly spaced apart mounting blocks 38 which are designed to avoid damping of the radial vibration of lthe ring, for example, by being formed of a flexible material, such as, rubber, and by being disposed adjacent `a node or nodes of the radial vibrations of ring 16.

The workpieces W, which are `shown in the form of circular wafers, for example, of germanium or silicon, are pressed downwardly against the radially vibrated upper annular `surface 39 4of ring 16 so that, when a lapping compound made up of 1a slurry -o-f suitable abrasive in oil, water or other liquid carrier, is supplied between surface 39 and the workpieces, the high frequency or ultrasonic radial vibrations of such lapping surface 39 will effect cavitatiion or violent agitation of 4the lapping compound and thereby cause the `abrasive of the latter to lap or polish the confronting or lower surfaces of workpieces W.

ln the lapping machine 1t?, the workpieces W are pressed downwardly :against the lapping suriace 39 by means of an annular pressure member 40 of substantial weight or mass resting on the top :surfaces of the workpieces. The annular pressure member 40 is preferably formed with upwardly directed rims 41 and 42. extending along its inner and outer penipheries to `define la shallow reservoir 43 for fthe abrasive slunry or lapping compound. The pressure member il further has a number of suitably spaced apart countersunk holes 44 through which the abrasive slurry or lapping compound passes from reservoir 43 for distribution between the lapping surface 39 and the confronting lower surfaces of the workpieces W. Since the lapping compound iloW-s continuously from reservoir 43, lthe supply of lapping compound in the latter is replenished through a pipe 45 extending from the outlet of a suitably driven pump 46 inthe lower compartment 15 and passing, in a sealed manner, through partition 12 to terminate in a downwardly directed nozzle or tap 47 disposed above reservoir 43 and controlled by a suitable valve 48. The lapping compound continuously supplied from the reiservoir 43 overflows from the lapping ring le onto the partition 12 and is drained from the latter by mean-s of a return pipe t9 which is joined through a T-Iconnection 5t) to `a pipe Sl extending to the inlet of pump 46. Thus, the lapping compound is continuously recirculated. rlhe lapping compound that is lost duning the normal lapping operation is replaced, as needed, through a pipe S2 extending from ia suitable source of fresh lapping compound to the T-connection 50 and having a suitable control valve 53 interposed therein.

The vertical movement of pressure member 4i) is guided by three equally spaced apart positioning pins 54 which are slidably received in downwardly opening bores 55 formed in member dil adjacent the outer periphery of the latter (FIG. 4), and the positioning pins 54 project upwardly from gauge blocks 56 which are :suitably secured on partition l2. The gauge blocks 56 are vertically dimensioned so that the upper surfaces thereof extend la distance above the lapping surface 39 lof ring 16 which is equal to .the desired finished thickness or height of the Workpieces W. Thus, when the lapping operation is initiated, the lower surface of pressure member 40 is spaced rom the upper surfaces of gauge blocks S6, as shown on FlG. 4. However, when the workpieces have been dapped and thereby reduced to the desired nal thickness 'or height, the bottom surface of member 4@ engages the upper surfaces of gauge blocks 6, as on PEG. l, and the downward pressure is relieved from the workpie'ces to, prevent any further substantial reduction in the thickness of the latter. After the pressure member 4d has engaged the gauge blocks 56, the lapping operation is preferably continued for a `short interval of time in order to make certain that all ofthe workpieces will be uniformly lapped to the desired thickness.

The upper or lapping surface 39 of the radially vibrated ring 16 is preferably formed with grooves, at least some of which extend at substantial angles to the directions of the radial vibrations. Thus, as shown on FIG. 6, the lapping surface of ring 16 may be formed with concentric circular grooves `57 which, at all points therealong, extend at right angles to the directions o-f the radial vibrations indicated by the arrows 58'. Alternatively, the grooves in the lapping surface may be in the form of a continuous spiral, as at 57a on the ring 16a. of FIG. 7, or the grooves may be arranged to form a grid, as at 57b on the ring 16h of FIG. 8. The grooves arranged in any of the patterns of FIGS. 6, 7 and 8 may have various cross-sectional shapes. Thus, as indicated at 57C on FIG. 9, grooves may be provided with substantially saw-tooth cross-sections dened between substantially vertical and inclined side walls. The vertical wall of each groove may be disposed at the radially outer side of the latter, as on FG. 9, or at the radially inner side of each groove, as in the case of the grooves 57d on PIG. l0. Where the lapping compounds used and the material of the workpieces permits, the grooves of the lapping surface may have substantially rectangular or square cross-sections, as at 57e on FIG. l1, or such grooves may have rounded bottom surfaces and be defined between parallel projections having rounded top surfaces, as in the case ofthe grooves 571, on FIG. 12.

The purpose of the described grooves formed in the lapping surface of the radially vibrated ring f6 is to promote the distribution of the lapping compound or abrasive slurry uniformly over the lapping surface thereby to ensure the uniform lapping action on the sur-faces of the porkpieces pressed thereagainst. Further, the grooves of the lapping surface serve to ensure the transmission of the high frequency or ultrasonic radial vibrations to the abrasive slurry, thereby to cause cavitation of the latter. Such cavitation causes the extremely high speed agitation or movement of the abrasive particles which thereby effect stock removal from the workpieces, while avoiding substantial wear of the lap plate. When the grooves have saw-tooth configurations, as in FIGS. 9 and 10, the high frequency radial vibrations occurring in the horizontal `plane cause the abrasive slurry impinging against the vertical side surfaces of the grooves to be directed against the lower surfaces of the workpieces and either radially inward, as in FIG. 9, or radially outward, as on FIG. 10', thereby to exert a positive pumping action on the abrasive slurry. By reason of such pumping action which causes gross movement of the lapping compound, a continuous flow of abrasive slurry over the lapping surface is maintained to ensure continuously efcient lapping action and a consequently high rate of stock removal.

lf the workpieces W remained stationary while being pressed against the grooved lapping surface of the ring i6 during high frequency radial vibration of the latter with an abrasive slurry applied between the lapping surface and the lower surfaces of the workpieces, then the configuration of the grooves of the lapping surface would be reproduced in the lower surfaces of the workpieces, as in the case of ultrasonic machining. Thus, smooth surfaces can be produced on `the workpieces by the ultrasonic vibrations only if the latter are substantially continuously moved over the grooved lapping surface during the entire lapping operation. It is apparent that such continuous movement of the workpieces cannot be conveniently effected during reciprocating movement thereof along a rectilinear path, as such reciprocating movement involves periods of dwell at the opposite ends of the stroke. Accordingly, in ultrasonic lapping machines embodying the invention, the workpieces are continuously moved along circular or orbital paths, thereby making necessary the employment of a lap plate in the form of a ring having an annular lapping surface which is radially vibrated, a-s previusly described herein. Since the amplitude of the radial vibrations at the annu-lar lapping surface may vary between the inner and outer peripheries of the latter, the circular or orbital paths of travel of the workpieces over the lapping surface are perferably eccentrically disposed with respect to the center of the lapping ring so that the surfaces of all of the workpieces are uniformly exposed to the portions of the lapping surface subjected to vibrations of relatively large and small amplitudes.

Referring now to FIGS. l and 2, it will be seen vthat the ultrasonic lapping machine lil effects the necessary continuous movement of the Workpieces W by means of a thin disc S9 having a thickness less than the desired finished thickness or height of the workpieces and being formed of a suitable plastic material which is substantially impervious to the eroding effects of the abrasive particles subjected to high frequency or ultrasonic vibrations. A suitable plastic material for the disc 59 is polyethylene terephthalate resin, which is available commercially under the trademark Mylar, but other plastic materials which are lsubstantially rigid and have high resistance to tearing when in the form of thin sheets or films may be used in place thereof.

The plastic disc 59 is formed with a circularly arranged series of spaced apart holes or openings 64B each adapted to receive one of the workpieces W with a substantial radial clearance 6l therebetween (FIGS. 2 and 4) so that the lapping compound or abrasive slurry falling on the plastic disc 59 through the holes 44 at the bottom of reservoir 43 can ilow through the clearances 6l for distribution between the lapping surface 35i and the lower surfaces of the workpieces.

As shown on FIG. l, the plastic disc 59 is disposed in a horizontal plane between the lap ring 16 and the pressure member 40 so as to avoid any interference with lapping of the workpieces while the latter are constrained to follow the movements of the disc '59 in a horizontal plane. In order to effect the desired movement of disc 59 in a horizontal plane, machine ltl further includes a vertical shaft 62 rotatably mounted, at is lower end, in a bearing structure 63 on the bottom wall 13 of housing 11 and having its axis of rotation concentric with the cen ter of the vibrated ring 16. A cylindrical head 64 is fixed on the upper end of shaft 62 and projects upwardly through a central opening in partition 12 where the head 64 is engaged by a suitable seal 65 in a retainer 66 so that the lapping compound cannot pass from the upper space spaanse 14 into the lower compartment 15. The head 64' has a i' diametrically extending, undercut groove 67 (FIGS. 1 and in its upper surface for adjustable attachments to the head 64 of a mounting 68 for the plastic disc 59.

As shown on FIG. 5, the mounting 63 includes a bolt 69 extending upwardly from the undercut groove 67 in which the head 7l) of the bolt is slidable, a bushing or sleeve 71 extending around the bolt 69 and a nut 72 tightened on the bolt 69 against the sleeve 71 so as to lock the latter at an adjustably determined distance from the center or axis of rotation of head da and shaft 62. An externally threaded collar '73 freely rotatable on the sleeve or bushing 71, and formed with a radially directed flange 74 at its lower end, extends upwardly in a central opening 75 of the disc 59. Finally, a ring nut 76 is screwed on threaded collar 73 to releasably clamp the disc 459 between flange 74 and nut 76. Thus, the disc 59 is mounted on head `64 and free to rotate relative to the latter with the center of rotation of the disc 59' being eccentrically located, by an adjustable distance, with respect to the axis of shaft 62, and hence the center of ring 16.

As shown on FIG. 1, shaft 62 is continuouslyr rotated during operation of the lapping machine by means of an electric motor 77 mounted lin compartment 15 and driving a variable speed drive 78 which, in turn, drives a bevel gear 79 meshing with a bevel gear 80 on the shaft 62.

As shaft `62 is rotated, the center of plastic disc 59 is moved along a circular path having a radius equal to the eccentricity of mounting 63 relative to the axis of shaft 62. Thus, all of the workpieces W are similarly moved continuously along circular paths on the lapping surface 39 of ring 16, which circular paths repeatedly bring the workpieces adjacent the inner and outer peripheral edges of the ring. A further advantage of the high frequency or ultrasonic vibrations imparted to the ring 16 is the consequent very substantial reduction thereby effected in the frictional resistance to movement of the workpieces W with .disc 59 relative to the ring 16. Thus, the forces at the edges of the openings 60 of disc 59 will not cause tearing of the latter even though the disc is very thin, as required in the case of the lapping of very thin workpieces, such las semiconductor elements. Further, since the reduction of the frictional resistance to movement of each of the workpieces, at any instant, is dependent, to a certain extent, upon the amplitude of the vibrations at the portion of the lapping surface then engaged by (the workpiece, and since substantially diametrically opposed workpieces engage portions of the lapping surface 39 at which vibrations of relatively small and relatively large amplitude are respectively encountered, for example, when the workpieces are positioned as on FIG. 1, the resulting different frictional yresistances to movement of the diametrically opposed workpieces entrained by the disc 59 tend to cause rotational movement of the latter on the sleeve or bushing 71. Thus, in addition to moving along circular paths, the workpieces W are further progressively displaced around the ring 16 so that, during extended operation of the machine 10, all portions of the lapping surface 39 are contacted by the workpieces to ensure that the limited Wear of the lapping surface is uniformly distributed.

Since the described movements of the workpieces carry the latter under the openings 44 in the pressure member 40 through which the abrasive slurry is distributed, it will be apparent that each of the workpieces periodically receives lapping compound on its upper surface. The supplying of lapping compound between the upper surface yof each workpiece W and the bottom surface of pressure member 40 causes the latter to act as an additional lap plate for lapping the upper surfaces of the workpieces in response to the movement of the latter by the disc 591 However, it will be apparent that the rate of stock removal during such lapping of the upper surfaces of the workpieces is substantially less than the rate of stock removal from the lower surfaces of the workpieces by reason of the high frequency or ultrasonic vibrations of ring 16 causing lapping of the lower surfaces. Thus, the machine 1@ embodying this invention makes possible the simultaneous lapping of the upper and lower surfaces of the workpieces at different rates of stock removal, and thereby functions in a manner not possible with any of the previously existing lapping machines.

Referring now to FIGS. 13 and 14, it will be seen that the ultrasonic lapping machine lil there illustrated is generally similar to the previously described machine lilv and differs substantially from the latter only with respect to the means provided for pressing the Workpieces against the radially vibrated lapping ring and for effecting the continuous movement of the Workpieces over the lapping surface of such ring. rl`he several parts of the machine 1li which correspond to parts of the machine 1t) are identified by the same reference numerals, but with a prime appended to each of them. rThus, it will be seen that, in the machine lil", the ring 16 is coupled to a vibration generating unit "17 so as to be radially vibrated and is suitably supported, as by blocks 33', above the horizontal partition 12 of the housing 11. Further, the abrasive slurry or lapping compound is supplied through a pipe lili and valve 48 to a tap or nozzle 47 which is `directed downwardly 'above the lapping surface of ring 16', while the abrasive slurry spilling over from the lapping surface and collecting on the partition 12 is drained through a return pipe 49. The lapping surface of ring lo is also preferably grooved, as previously described herein with respect to FiGS. 6 to l2, so las to improve the distribution of the lapping compound and the rate of stock removal from the workpieces.

ln the machine lll', the vertical shaft o2 driven through the gears 79 and 89 and being rotatably supported, at its lower end, in a bearing struc-ture at the bottom of housing 11', extends upwardly through the seal 65 carried by partition 12' and, at its upper end, is also journalled in a bearing structure 81 carried by ran overhead frame S2 extending from the top of housing r11. A support table E53 is fixed on shaft `62 at a level substantially above the radially vibrated ring 16 and carries a plurality, for example four as shown, of fluid pressure operated cylinders 3d which are equally spaced `apart around the support table S3 land have their axes extending vertically. The piston rods S5 of the fluid pressure operated cylinders 84 extend downwardly from Itable 83 (PEG. 13) and, at their lorwer ends, carry freely rotatable pressure discs S6. Each pressure `disc 3o is freely slidable in an externally toothed gear ring 87 which rests on the surface of ring 15 and meshes with a xed, internally toothed gear ring 3S which is secured to the housing 11', as by brackets 39 (FIG. 14). A circular pad @il (FIG. 13) of felt, rubber' or other compressible material fits closely in each gear ring 57 under the related pressure disc 85 and bears downwardly on the Workpieces W lwhich .are held in spaced apart relationship within the gear ring 37 by means of a thin plastic disc 91 having openings in which the worlrpieces are located;

When preparing the lapping machine 1li for operation, fluid under pressure is supplied to the lower ends of the cylinders `34', so as to raise 'the pressure discs 86. The workpieces W, plastic locating discs 91 and pads 9i) are then `disposed in each of the gear rings 87 so that, when fluid under pressure is supplied to the cylinders 84 to move the pressure discs 86 downwardly, each disc 85 presses the related pad 9@ onto the workpieces for holding the latter against the lapping surface of ning 16'. VThe pressure thus exerted on each pad 9G tends to radially expand the latter into tight engagement with the interior surface of the related gear ring 87 so that the pad 9) and the related nest of workpieces will be constrained to rotate with the gear ring d? about the vertical axis of the piston rod 35.

When shaft 62. is rotated `and thereby turns the support table 33, the centers of the gear rings 87 move along a circular path which is concentric with the center of ring 16', as indicated by the arrow 92. on FIG. 14, and, during such movement of the gear rings 37, the latter further turn about their individual centers, as indicated by the arrows 93 on FIG. 14, by reason of the meshing engagement of the teeth of each gear ring 87 with the -iiXed ring gear 3S. Thus, each workpiece W moves along a circular path concentric with the axis of the related piston rod d5 While such aXis simultaneously moves along a circular path concentric with the center of ring 16'. By reason of such movements of the workpieces, all portions of the lapping surface of ring 16', are uniformly contacted by each workpiece during extended lapping operation, thereby to ensure that uniform lapping of the workpieces is achieved Iand funther that the limited wear of the lapping surface of ring i6 will be uniformly `distributed over the latter.

In each of the illustrated machines lil Iand lil', a single vibration generating unit ll' or ll7 is coupled to the lapping ring 16 or le for eifect-ing radial vibration of the latter. However, it is `apparent that a plurality of vibration generating units which are suitably phased may be coupled to the periphery of the lapping ring at spaced apart locations therealong to produce the desired radial vibnation of the lapping ring. It is also apparent that two radially vibrated lapping rings may be provided to simultaneously lap the top and bott-om surfaces of 'Worltpie'ces disposed therebetween, or to simultaneously lap surfaces of -workpieces interposed between the two vibrated lapping rings and a central pressure plate disposed between the lapping rings. Conversely, a single vibrated lapping ring may be positioned between upper and lower pressure plates to simultaneously lap workpieces disposed between the pressure plates and the top and bottom surfaces of the Vibrated ring.

The criteria for determining the dimensions of the lapping ring may be summarized as follows:

A circular ring i6 or le with a concentric circular opening or bore and rectangular cross-section as shown, has two families of resonance modes with displacement vectors parallel to the planes of the surfaces of the ring. The extensional (radial) vibration of a closed ring can be roughly compared with the longitudinal vibration of a solid cylinder with a curved longitudinal axis to give equations for the radial displacement u and for the displacement w tangential to the circumference of the ring as follows:

(l) u(@t)=(Asin n-l-B cos n0) cos (wt-l-go) (2) w( 9!) :11(A cos :15P-B sin nd) cos (wt-i-(p) where tztime f=frequency 0=angle coordinate p=phase angle A and B are amplitude constants Equations l and Z show that u and w are in phase, that the maxima of Equation l coincides with the zeros of Equation 2 and vice versa, and that, with increasing values of n, the tangential displacement becomes predo1ninant. Thus, the case n=ll is of special interest for, in that case, the vector w vanishes while the vector u becomes independent of the angle 0.

When the ring .le or le is designed for nzll, the surfaces of the ring vibrate strictly in the radial direction and with uniform amplitude along the circumference, although there are variations in amplitude along radial lines. The variations in amplitude along radial lines are increased by increasing the difference between the outer diameter (D) of the ring and the inner diameter (d) thereof so that, if the central hole is eliminated from the ring 16 or le', the amplitude is zero at the center of the rmg.

The resonant frequencies fn for the extensional (radial) modes of the ring i6 or 16 are represented by the following:

Further, the medium diameter Dm of the ring is indicated by the following formula:

(4) Dm=Lvl+n2 where:

AL is the wavelength of the longitudinal vibration for the selected frequency in a bar having the same crosssection as the ring.

In the case where 11:0 (the lowes-t extensional mode), Formula 4 transforms into: Y

which means that, for the lowest extensional mode 11:0) where only radial vibrations of uniform amplitude occur at the surfaces of the ring, the medium circumference (that is, the circumference of the ring at the medium diameter) is equal to one longitudinal wavelength in a bar of the same cross-section at the lowest resonant frequency.

Although illustrative embodiments `of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modilications in addition to those mentioned above may be effected therein by one skilled in the art without departing from the scope or spirit of the invention, except as defined in lthe appended claims.

What is claimed is:

l. A lapping machine comprising (A) a circular ring having an annular lapping surface,

(B) vibration generating means coupled to said ring -to effect radial vibration of the latter at a high frequency,

(C) means for pressing the workpieces to be lapped against said lapping surface, and

(D) means for supplying an abrasive slurry in between said lapping surface and the surfaces of the workpiece pressed thereagainst so that said high frequency vibrations cause the abrasive .to smoothly finish said surfaces of the workpieces.

2. A lapping machine comprising (A) a circular ring having an annular lapping surface,

(B) vibration generating means coupled to said ring to effect radial vibration of the latter at a high frequency,

(C) means for pressing the workpieces to be lapped against said lapping surface,

(D) means for supplying an abrasive slurry in between said lapping surface and the surfaces of the workpieces pressed thereagainst so that said high frequency vibrations cause the abrasive to smoothly finish said surfaces of the workpieces, and

(E) means for effecting continuous movement of the workpieces over said lapping surface along circular paths having their centers spaced substantially from the center of said ring.

3. A lapping machine comprising (A) means generating high frequency, longitudinal vibrations,

(B) a circular ring having an annular lapping surface and being coupled to said generating means to ll i radially receive said longitudinal vibrations from the latter, said ring having a medium circumference which is equal to one longitudinal Wavelength of sound in a bar of the same material and crosssection at said frequency ofthe vibrations so that said ring is made to vibrate radially,

(C) means for pressing the workpieces to be lapped against said annular lapping surface of the radially vibrated ring, and

(D) means for supplying an abrasive slur-ry in between said lapping surface and the surfaces of the workpieces pressed thereagainst so that said high frequency vibrations cause the abrasive to smoothly finish said surface of the worlipieces.

4. A lapping machine comprising (A) means generating high frequency, longitudinal vibra/tions,

A (B) a circular ring having `an `annular lapping surface yand being coupled to said `genera-ting means to radially receive said longitudinal vibrations :from the latter `so that said ring is made to vibrate radially at said high frequency, said lapping surface having grooves therein which extend, at least in part, at substantial angles to the directions of the radial vibrations,

(C) means for pressing the workpieces to be lapped against said annular lapping surface, and

(D) means for supplying an abrasive slurry to said lapping surface from above so that said grooves promote the uniform distribution of the slurry between said lapping surface and the confronting surfaces of the workpieces and further promote icavitation of the slurry for rapid stock removal from the worltpieces in response to the radial vibration of said ring.

5. A lapping machine as in yclaim 4;

wherein said grooves in the annular lapping surface are in the form of concentric circles.

6. A lapping machine as in lclaim 4;

wherein said `grooves extend spirally in said annular lapping surface.

7. A lapping machine as in claim 4;

wherein said grooves extend at right angles to each :other in a grid pattern.

8. A lapping machine as in claim 4;

wherein each of said grooves has `one side wall perpendicular to the plane of said lapping surface and its other side wall inclined with respect to said plane so as to `develop a generally radial pumping action on the slurry in response `to said radial vibrations.

9. A llapping machine comprising (A) means generating high frequency, longitudinal vibrations,

(B) a cir-cular ring having an annular lapping surface and being coupled to said generating means to radially receive said longitudinal vibrations from the latter so that said ring is made to vibrate radially at said high frequency, said lapping surface having `grooves therein which extend, at least in part, at substantial angles to` the directions of the radial vibrations, f

(C) means for pressing the workpieces to .be lapped against said annular lapping surface,

(D) means for supplying an abrasive slurry to said lapping surface from above so that said Igrooves promote the uniform distribution of the slurry between said lapping surface and the confronting surfaces of the workpieces and further promote cavitation Iof the slurry for rapid stock removal from the workpieces in response to the radial vibration `of said ring, and

(E) means for effecting continuous movement of the workpieces over said lapping surface along circular paths having their centers spaced substantially from the `center of said ring.

l0. A lapping machine comprising (A) means generating high frequency, longitudinal vibrations,

(B) a Icircular ring having an annular lapping surface and being coupled to` said generating means to radially receive said longitudinal vibrations from the latter,

(l) said ring having a medium circumference which is one longitudinal wavelength of sound in a bar of the same material and cross-section at said high frequency of the vibrations so that said ring is radially vibrated uniformly around its circumference,

(2) said lapping surface of the radially vibrated ring having grooves therein which extend, at least in part, at substantial angles with respect to the radial vibrations of the ring,

(C) means for pressing the workpieces to be lapped against said annular lapping surface,

(D) means for supplying an abrasive slurry to said lapping surfacefrom above so that said grooves promote the uniform distribution of the slurry between said lapping surface and the confronting surfaces lof the workpieces and further promote cavitation of the slurry for rapid stock removal from the workpieces in response to the radial vibration of said ring, and

(E) means for effecting continuous movement of the workpieces over said lapping sur-face along circular paths having their centers spaced substantially from the center of said ring.

1l. A lapping machine as in lclaim l0;

wherein said ring lies substantially in a horizontal plane, and

wherein said means lfor pressing the workpieces against said lapping surface includes a metal member of substantial weight having a flat bottom surface resting on top of the workpieces.

l2. A lapping machine as in claim ll;

further .comprising means slidably engageable with said metal member resting on top of the workpieces to prevent rotation thereof, and gauge bloclts in lixed positions relative to said ring and being enga-ged from above by said flat :bottom surface of the metal mem- -ber to prevent further `downward movement of the [latter when the thickness of the Workpieces is reduced to a predetermined dimension.

13. A lapping machine as in claim l2;

wherein said metal member defines `a reservoir for the abrasive slurry having discharge openings at said at `bottom surface, and said means for supplying an abrasive slurry opens into said reservoir so that, during the movement lof the workpieces over the lapping surface, the top surfaces of the workpieces periodically receive abrasive slurry from said discharge openings and are lapped by said flat bottom surface of said mem-ber resting thereon.

14. A lapping machine as in claim l0;

wherein said means `for effecting continuous movement of the wonkpieces over the lapping surface includes (a) a rotated shaft concentric with said ring,

(b) a thin plastic disc disposed above said lapping surface and having a series of openings therein each receiving a workpiece, and

(c) mounting means connecting said disc to said shaft with said disc being free torotate about its center and having the latter spaced radially from the axis `of `said shaft.

l5. A lapping machine as in claim l0;

wherein said means for effecting continuous movement of the worrtpieces over the lapping surface includes (a) a support structure rotated coaxially with the ycenter of said ring,

(b) a plurality of gear rings resting on said lapping surface and rotatably coupled to said support structure with the axes of said gear rings 13 `'being spaced from the axis of rotation of said support structure, each of said gear rings having a nest of workpieces positioned therein, and (c) a fixed, internally toothed ring gear meshing with said gear rings to turn the latter `about said axes of the gear rings in response to the movement Iof the latter with said support structure about said axis of rotation of the latter.

16. A lapping machine comprising (A) magnetostrictive transducer means operative to generate longitudinal vibrations at a frequency in the range `between 10,000 and 100,000 cycles per second,

(B) a circular ring having an annular lapping surface,

(C) means transmitting the longitudinal vibrations from said transducer means radially into said ring so -as to cause radial vibration of the latter at said frequency,

(D) means supporting s-aid ring substantially at nodes of the radial vibration of the latter and disposing said lapping surface in a horizontal plane at the top of said ring,

(E) means for pressing the Workpieces to be lapped downwardly -against said lapping surface, and

(F) means for supplying an abrasive slurry to said lapping surface so that the radial vibration of said ring causes the abrasive to lap the surfaces of the workpieces pressed against said lapping surface.

17.y A lapping machine as in claim 16;

wherein said lapping surface of the circular ring has grooves therein which extend, at least in part, at substantial `angles with respect to the directions of the radial vibrations of the ring, and

further comprising means for effecting continuous movement of the -workpieces over said lapping surface along circular paths having their centers spaced from the center of said ring.

i18. A lapping machine as in claim 17;

wherein said means for effecting continuous movement of the workpieces over the lapping surface includes (a) a rotated shaft concentric with said ring,

(b) ya thin plastic disc disposed above said lapping surface and having a series of openings therein each receiving a workpiece, and

(c) mounting means connecting said disc to said shaft with said disc .being -free to rotate about its center and having the latter spaced radially from the axis of said shaft.

19. A lapping machine as in claim 17 wherein said means for eifecting continuous movement of the Workpieces over the lapping surface includes (a) a support structure rotated coaxially with the center of said ring,

(b) ra plurality of gear rings resting on said lapping surface and rotatably coupled to said support structure with the axes of said gear rings being yspaced Ifrom the axis of rotation of said support structure, each of said gear rings having a nest of Workpieces positioned therein, and

(c) a xed, internally toothed ring gear meshing with said gear rings to turn the latter about said axes of the gear rings in response to the movement of the latter with said support structure about said axis of rotation of the latter.

References Cited in the le of this patent UNITED STATES PATENTS 2,340,843 Bailey Feb. 1, 1944 2,410,752 Sells et al. Nov. 5, i1946 2,736,144 Thatcher Feb. 28, 1956 2,772,521 Voytech Dec. 4, 1956 2,854,795 McCown et al. Oct. 7, 1958 2,870,580 Norton Jan. 27, 1959 2,922,264 Mushruch lan. 26, I1960 2,944,375 Lipkins Ian. 12, 1960 2,979,868 Emeis Apr. 18, 19611 3,027,689 Merkl et al Apr. 3, 1962 

1. A LAPPING MACHINE COMPRISING (A) A CIRCULAR RING HAVING AN ANNULAR LAPPING SURFACE, (B) VIBRATION GENERATING MEANS COUPLED TO SAID RING TO EFFECT RADIAL VIBRATION OF THE LATTER AT A HIGH FREQUENCY, (C) MEANS FOR PRESSING THE WORKPIECES TO BE LAPPED AGAINST SAID LAPPING SURFACE, AND (D) MEANS FOR SUPPLYING AN ABRASIVE SLURRY IN BETWEEN SAID LAPPING SURFACE AND THE SURFACES OF THE WORKPIECE PRESSED THEREAGAINST SO THAT SAID HIGH FREQUENCY VIBRATIONS CAUSE THE ABRASIVE TO SMOOTHLY FINISH SAID SURFACES OF THE WORKPIECES. 